[PATCH] x86-64: Clean up the early boot page table

[PATCH] x86-64: Clean up the early boot page table

- Merge physmem_pgt and ident_pgt, removing physmem_pgt.  The merge
  is broken as soon as mm/init.c:init_memory_mapping is run.
- As physmem_pgt is gone don't export it in pgtable.h.
- Use defines from pgtable.h for page permissions.
- Fix the physical memory identity mapping so it is at the correct
  address.
- Remove the physical memory mapping from wakeup_level4_pgt it
  is at the wrong address so we can't possibly be usinging it.
- Simply NEXT_PAGE the work to calculate the phys_ alias
  of the labels was very cool.  Unfortuantely it was a brittle
  special purpose hack that makes maitenance more difficult.
  Instead just use label - __START_KERNEL_map like we do
  everywhere else in assembly.

Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: Vivek Goyal <vgoyal@in.ibm.com>
Signed-off-by: Andi Kleen <ak@suse.de>